The present invention relates to an improvement in information storage systems, and especially in the means for providing constant rotation to the disc on which data is stored.
Overall disc drive size is a paramount concern to the drive design engineers. As smaller, light weight portable computers have grown in demand, their engineers have continually searched for ways to reduce both the overall size, weight and internal friction of the disc drive while maintaining or improving overall drive performance.
Present spindle motor technology is typically a multi-phase brushless DC motor which has been designed for long life at constant rotational speeds. However, such motors, while designed with increased sophistication, still occupy a major percentage of the overall internal envelope of the disc drive. Typically, such spindle motors extend below the envelope where the discs are rotating, with rotating discs supported on a hub on the top of the spindle motor. Obviously, this significantly increases the overall height of the drive. The alternative approach is to use what is called an in hub spindle motor, where both the motor, rotor and stator are incorporated within the hub of the disc. This dramatically reduces the height of the drive; however, it must necessarily increase the diameter of the hub, resulting in a net loss in data storage space on the surface of the disc.
The problem left unresolved by such approaches therefore is to provide a motor within the defined disc drive envelope which imparts constant rotational speed to the spinning discs, while minimizing the amount of internal disc drive space which must be devoted to the mechanics of the spindle motor.